This invention relates to a heat/pressure applying unit incorporated in, for example, a color copying apparatus or the like and, more particularly, to a mechanism for preventing a recording medium from winding around a pair of rollers of the heat/pressure applying unit.
Conventionally, there is known a Xerographic copying apparatus which has a heat-fixing unit composed of a pair of rollers. One of the pair of rollers is formed by a silicone rubber roller. The other roller has a heat pipe and a halogen lamp arranged along an axis of the heat pipe. Toner transferred onto an ordinary sheet of paper is caused to pass through a nip between the heat pipe and the silicone rubber roller so that the toner is melted and fixed onto the ordinary sheet. Since the toner has adhesiveness when melted, the roller in contact with the toner is formed of silicone rubber superior in stripping ability.
In order to prevent the sheet from adhering to the silicone rubber roller, a plurality of stripper claws are arranged in a single row in spaced relation to each other along an axis of the silicone rubber roller. Each stripper claw is formed of heat-resistant resinous material, and has an acute forward end. The forward ends of the respective stripper claws get into between the silicone rubber roller and the sheet tending to adhere to the silicone rubber roller, to strip the sheet forcibly from the silicone rubber roller.
In case of the use of a recording medium higher in adhesiveness than the ordinary sheet of paper, such as, for example, a developer sheet having its one side coated with a developer agent, however, the following problem arises. That is, when the developer sheet having carried thereon an image is caused to pass through the nip between the heat pipe and the silicone rubber roller of the heat-fixing unit to promote color development of the developer sheet, the developer sheet frequently winds around the silicone rubber roller, because the adhesiveness of the developer agent melted is stronger in adhesion force than the toner.
Furthermore, the developer agent side of the developer sheet is extremely liable to be marred as compared with the ordinary sheet having carried thereon the toner. In addition, the higher the environmental humidity, the stronger the developer sheet tends to wind around the silicone rubber roller. If the developer sheet winds around the silicone rubber robber, the sheet is brought to high temperature. Thus, there are fears that the developer sheet is burnt and component parts of the heat-fixing unit are damaged.